.TH std::hash 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::hash \- std::hash

.SH Synopsis
   Defined in header <filesystem>
   template<>                           \fI(since C++17)\fP
   struct hash<std::filesystem::path>;

   The template specialization of std::hash for std::filesystem::path allows users to
   obtain hash values of std::filesystem::path.

   The operator() of this specialization is noexcept. For every std::filesystem::path
   value p, std::hash<std::filesystem::path>{}(p) is equal to
   std::filesystem::hash_value(p).

   This specialization was absent from the C++17 standard publication, see LWG issue
   3657.

.SH Example


// Run this code

 #include <cassert>
 #include <cstddef>
 #include <filesystem>
 #include <iomanip>
 #include <iostream>
 #include <unordered_set>
 namespace fs = std::filesystem;

 void show_hash(fs::path const& p)
 {
     std::cout << std::hex << std::uppercase << std::setw(16)
               << std::hash<fs::path>{}(p) << " : " << p << '\\n';
 }

 int main()
 {
     auto tmp1 = fs::path{"/tmp"};
     auto tmp2 = fs::path{"/tmp/../tmp"};
     assert(!(tmp1 == tmp2));
     assert(fs::equivalent(tmp1, tmp2));
     show_hash(tmp1);
     show_hash(tmp2);

     for (auto s : {"/a///b", "/a//b", "/a/c", "...", "..", ".", ""})
         show_hash(s);

     std::unordered_set<fs::path, std::hash<fs::path>> dirs{
         "/bin", "/bin", "/lib", "/lib", "/opt", "/opt", "/tmp", "/tmp/../tmp"};
     for (fs::path const& p : dirs)
         std::cout << p << ' ';
     std::cout << '\\n';
 }

.SH Possible output:

 6050C47ADB62DFE5 : "/tmp"
 62795A58B69AD90A : "/tmp/../tmp"
 FF302110C9991974 : "/a///b"
 FF302110C9991974 : "/a//b"
 FD6167277915D464 : "/a/c"
 C42040F82CD8B542 : "..."
 D2D30154E0B78BBC : ".."
 D18C722215ED0530 : "."
                0 : ""
 "/tmp/../tmp" "/opt" "/lib" "/tmp" "/bin"

.SH See also

   hash       hash function object
   \fI(C++11)\fP    \fI(class template)\fP
   hash_value calculates a hash value for a path object
   \fI(C++17)\fP    \fI(function)\fP
